Transcript ppt

Last section!
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Project 4 + EC due tomorrow
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Today:
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Project 4 questions
Some practice for the exam
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“Big picture” review tomorrow
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Evaluations
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Project 3 + all old stuff back
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Project 3 average: 52/55
Great job
You will get project 4 grades by email
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Project 4 questions
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Filename length?
File size?
General?
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Review: file systems
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Two improvements BSD Fast File System
implemented?
Name the type of system and workload
that LFS was based on
Calculate max UNIX file size for 1K blocks
The sequence of actions that occurs when
a user executes the following, in terms of
inodes and directory entries:
touch file && ln file file2 && rm file && rm file2
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Review: file systems
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Two improvements BSD Fast File System
implemented?
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Name the type of system and workload that LFS
was based on
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Frequent writes with lots of small files
Max UNIX file size for 1K blocks?
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Cylinder groups, blocksize 1->4K, disk params
(12+256+256^2+256^3)*1K = around 16 GB
The sequence of actions that occurs when a user
executes the following, in terms of inodes and
directory entries: touch file && ln file file2
&& rm file && rm file2
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…
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Review: virtual memory
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Segmentation doesn’t have this problem of
wasted space.
How does copy-on-write work? What is it
used for?
What is Belady's anomaly?
What is Belady’s algorithm?
Give the number of memory references the
first load will produce on x86 on powerup.
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Review: virtual memory
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Segmentation doesn’t have this problem of
wasted space.
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How does copy-on-write work? What is it used
for?
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Bad property of FIFO – fault rate can increase with more
allocated frames
What is Belady’s (OPT) algorithm?
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…
What is Belady's anomaly?
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Internal fragmentation
Optimal page replacement – evict page the won’t be
needed longest into the future
Number of references the first load will produce
on x86 on powerup.
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Two-level PT: 3 (assuming paging enabled)
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People do not program the Belady’s page
replacement algorithm today because:
a) it is too expensive to build the hardware
support
b) it is impossible to do so
c) page replacement costs are not sufficiently
high for optimality to be a significant concern
d) there exist better-performing page
replacement algorithms
e) This policy are only applicable in computers
that support page reference bits within the
PTE. Not all processors do so.
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synchronization
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The best reason to use semaphores rather
than busy-waiting in a user-level program
is:
a) decreases the chance of deadlock
b) decreases the chance of livelock
c) allows more different types of synchronization
to be coded
d) avoids wasted processor cycles
e) avoids expensive context switches
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True/false: good style dictates that a thread
performing a P on a semaphore should always be
the thread performing the corresponding V on
that semaphore
When monitors are used for synchronization and
access to shared data:
a) True/False: deadlock becomes impossible
b) True/False: race conditions on access to that data
become impossible
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Consider a modern desktop computer on
which the hard disk is spinning. The more
significant delay in reading from a 4K byte
file that has not been accessed in a long
time is:
a) context switch to enter the operating system
b) time spent in the OS to determine what disk
blocks to fetch
c) latency awaiting disk arm movement
d) latency awaiting disk rotation
e) transfer time
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Four out of the five of these instantiate a
single basic principle. But the fifth one is
essentially unrelated. Which is the
unrelated one?
a)
b)
c)
d)
e)
processor (L2) cache
disk buffer pool
page table
translation lookaside buffer
DNS cache
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Which of the following are not typically
saved when a process issues a system call
that blocks, causing a context switch to
some other process:
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contents of registers
program counter value
interrupt vector table
name of the process that was executing
elapsed time since process last started
executing
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Which of the following abstractions are
implemented entirely in the kernel of an
OS like Linux:
a) remote object invocation and remote
procedure call
b) the process abstraction
c) dynamically linked libraries (DLLs)
d) the window manager
e) public key encryption/decryption
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T / F A microkernel is a category of
operating systems designed for sensors or
other forms of micro-processors.
T / F A priority inversion is said to occur if
a higher priority task is waiting for a lowerpriority task to perform some action.
How can you detect someone stole your
password?
Why does Windows require ctrl+alt+del
before you type your username/password?
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Last slide
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Good luck on the exam!
Congratulations on making it through a
tough class 
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